Korps,
 Technically there is nothing wrong with using a reversing Y-harness, but this is a situation where you simply don't need one. It's something that doesn't need to be purchased, and it's also one more thing that can go wrong as well. But if you want to use one there is no reason why you can't. You just have to hook up your ailerons differently. Normally you would hook them up like the diagram I posted above, with the linkages connected on opposite sides of the servos. If you are using a reversing Y-harness then you would hook them up on the same side of the servos.

Ken